1. Field of the Invention
The present invention relates to an optical shutter for a plasma display panel and driving method thereof. More particularly, the present invention relates to an optical shutter for a plasma display panel in which the optical shutter that can be selectively driven according to the electrowetting phenomenon is formed on a light-emitting unit of the plasma display panel, and the optical shutter is opened only during a display period, whereby contrast is improved, and a driving method thereof.
2. Background of the Related Art
Recently, the size of a plasma display panel (hereinafter, referred to as ‘PDP’) being a large-screen digital wall mount type television has increased from 30 to 76 inches. PDP manufacturers are in keen competition with one another in order to realize the low price.
A PDP device, which has been spotlighted as a next-generation display device along with a TFT LCD, organic EL, FED and the like, is a display device that employs a light-emitting phenomenon generating due to a difference in energy when red (R), green (G) and blue (B) phosphors return from an excited state to a ground state if the phosphors are excited with ultraviolet of 147 nm generated during the discharge of a gas such as He+Xe or Ne+Xe within discharge cells isolated by barrier ribs.
This PDP can have a variety of structures depending on its implementation method. However, most of the PDPs have a similar structure in which an electrode bus for driving each cell is disposed and a phosphor layer to be light-emitted by each cell is coated in cell regions isolated by barrier ribs.
FIG. 1 is a perspective view illustrating the construction of a common AC type PDP device.
A lower plate of the PDP includes address electrodes 2 of discharge cells, which are formed on the top surface of a lower glass substrate 1, a lower dielectric layer 3 formed on the entire address electrodes 2, barrier ribs 4, which are formed on the dielectric layer 3 and isolate the discharge cells, and phosphor layers 5 that are formed on the dielectric layer 3 and isolated by the barrier ribs 4. The dielectric layer 3 or the barrier ribs 4 can include some reflection materials for reflecting a visible ray generated by the phosphor layers 5. A shield film for preventing infiltration of alkali ion contained in the glass substrate 1 can be formed on the lower glass substrate 1.
Furthermore, an upper plate of the plasma display panel includes transparent electrodes 12 formed on the bottom surface of an upper glass substrate 11, bus electrodes 13 that lower resistance values of the transparent electrodes 12, a dielectric layer 14 formed on the entire top surface of the upper glass substrate 11, including the transparent electrodes 12 and the bus electrodes 13, and a protection layer 15 which is formed on the entire surface of the dielectric layer 14 and protects the dielectric layer 14 depending on plasma discharging. The upper plate formed thus is disposed so that the protection layer 15 faces the barrier ribs 4 and the phosphor layer 5 of the lower plate.
In the construction of the upper plate of the conventional plasma display panel, electrodes composed of a pair of the transparent electrode 12 and the bus electrode 13 operate as a scan electrode and a sustain electrode, and generate a discharge due to a difference in voltage provided thereto. In this time, the phosphor layer 5 within the discharge cell is excited by ultraviolet generated, thus generating a visible ray. In this case, the plasma display panel implements the gray scale necessary for displaying an image by controlling a discharge sustaining period depending on video data, i.e., the number of a sustain discharge.
A method of driving such a plasma display panel usually employs an ADS (Address and Display Separation) driving method in which the device is driven with it being divided into a screen non-display period and a screen display period, i.e., a discharge sustaining period. In the ADS driving method, one frame is divided into the n number of bits, and each of sub-fields is divided into a reset period, an address period and a sustain period.
In this time, the reset period is a period where an initial condition is set so that next addressing is possible. In this period, wall charges are allowed to have a constant state right before the address period in order for each cell to operate stably with uniform brightness.
The address period is a period where cell to be turned on and cells to be turned off are selected according to a data pulse. The sustain period is a period where a discharge for cells which are turned on in the address period is maintained.
The screen is not displayed during the reset period and the address period. In this connection, this can be called a ‘non-display period’. Furthermore, the screen is displayed during the sustain period. Thus, this can be called a ‘display period’.
Accordingly, the period where the screen is actually displayed is a discharge sustain period, i.e., a screen display period. It will be an ideal one that during the reset and address periods where cells to be discharged are selected before the sustain period, emission due to the discharge is not generated. However, actually, since cells of the whole panel region are initialized during the reset and address periods, a weak discharge is generated. This causes the black brightness of the panel to increase. Accordingly, the contrast characteristic of an image is degraded and the clearness is thus lowered.
As stated previously, the conventional plasma display panel employs the driving method in which the device is driven with it being divided into the non-display period where cells to be discharged are initialized and selected and the display period where a discharge is sustained and the screen is thus displayed. This makes contrast degraded because the weak discharge is generated in the non-display period where the screen is not displayed actually. Accordingly, there are problems in that the clearness decreases and the display quality is degraded accordingly.